The pigment that gives red cabbage its color is called anthocyanin. It is also the pigment found in leaves that turn red or purple in the fall. Anthocyanin is a good indicator of acids and bases, as you saw from the changing colors in this experiment. When added to a base, the purplish pigment turns green or yellow and when added to an acid, it changes to pink or red. In something that is neutral (neither an acid nor a base), the paper will remain the same color (or maybe turn a little blue).